Telephone system



March 24, 1925.

E. E. HINRI'CHSEN TELEPHONE SYSTEM 4 Sheets-Sheet 1 In veq'ior: [awardE. Hmn'c/zsen March 24, 1925.

E. E HINRICHSEN TELEPHONE sY sTEM' 4 Sheets-Sheet 2 b E 1?. new/2 my.

E. E. HINRICHSEN TELEPHNE s'Ys TEM 4' Sheets-Sheet 5 March 24, 1925.1,531,006

E. E. HINRICHSEN TELEPHONE SYS TEM Fil Jan. l3, 1921 4 $heets-$heet 4 Taa Patented Mar. 24, 1925.

1,531.,Qtt

UNITED STATES PATENTOFFICE.

EDWARD E. HINRICHSEN, or NEW YORK, N. ASSIGNOR To WESTERN ELECTRICCOMPANY, INCORPORATED, on NEW YORK, N. Y. ACORPORATION on NEW YORK.

T LEPHONE SYsTEM.

Application filed January 13, 1921. Serial No. 436,884.

To all whom it may concern Be it known that I. EDWARD E. HINRIOH sEN, acitizen of the United States,residing at New York, in the county of NewYork,

State of New York. have invented certain new and useful Improvements inTelephone Systems. of which the following is a full, clear, concise, andexact. description.

This application relates to telephone systems and particularly tomachine switching systems of the type in which relay mechanisms areemployed for interconnecting the calling and called subscribers.

it feature of the invention is a new method for controlling thechange-over from one brush to another by the direction switch employedfor piloting the connec-' tions.

Another feature of the invention resides in the use of a directionswitch by the attendant subscriber in place of the individual lineselecting keys heretofore used in systems of this nature. By the use ofsuch a direc tion switch the complete operation of this 5 system is mademore uniform and the num' ber of devices under the control of theattendant operator is greatly reduced.

Another feature of the invention is a means whereby the attendantoperator may set up a connection to a busy line and leave it in such acondition that the line will be automatically seized when the busycondition is removed.

Another feature of the invention is a new 5 arrangement for signallingthe central office when the battery supply for the system fails. Thedrawings comprise a diagrammatic representation of a preferred means forcarrying out the invent-ion. There are four figures which, when placedtogether, Figure 2 below Figure 1, Figure 3to the right of Figure 2 andFigure 4; above Figure 3 and to the right of Figure 1, form a completecircuit diagram. Figure 1 contains a representation of two groups orsubscribers lines together with the necessary relays for connecting saidlines to acentral ottice trunk line; Figure 2 shows the means forconnecting the said lines to a link circuit, and a link circuit to thesaid lines; Figure 3 Shows a link circuit together with severalauxiliarycircuit-s such as the ringing circuit, the busy tonecircuitand thebuzzer circuit; and Figure 4 shows a' central office trunk line.

In the drawings, a system of about eighty lines capacity is represented.A call'from one station to another is made bydialing the number ofthecalled station. An originating call to the central office is made bydialing the central office code which connects the calling station tothe central'oiiice so thatthe subscriber may give thedesired number tothe operator thereat. The disconnect signal is given to the centraloflice when the calling subscriber hangs up. The calling subscriber canalso flash the operator' by manipulating hisswitchhook in the'lusualmanner.

An incoming call is received by the attendant subscriberand may beextended to any desired station by the operation of her calling dial.The supervisory relay at the central office is operated as soon as theattendant answers the call and remains operated until the called stationhas answered and hung upagain or until the attendant subscriber operatesa disconnect key incase the call is not extended to a station. Adisconnect signal is given to the central oiiice automatically when thecalled subscriber hangs up at the end of the conversation but provisionis made for the called subscriber to signal the attendant if desired.

Calls to the central oflice may be 0rigi nated by the attendant andextended to any desired station.

The link circuits to be usediin establishing local connections arenotused on central office connections. 5 Each trunk is provided withapparatus for connecting directly to any line and whena callingsubscriber dials the central *oflice code the link circuit to which hewas originally connected functions to select an idle trunk and connectsit to his line and then releases ready for use on another connection.

Provision isma'de for preventing any line from calling the centraloffice directly. Incoming calls may, however, be completed to suchlines.

The circuit arrangements are such that the connection links are used in.rotation. A linkhaving once been selected remains busy to incoming callsuntil all the other link circuits have been used even though it has beenreleased in the mean time.

If the link circuit-selected by anincoming call fails to pick up thecalling line the call is transferred after a brief interval to'the natea call to the central oflice thus avoiding double connections. t, a

The detailed operation of the individual circuits shown on the drawingis as follows:

Line circuit.

TWhen a subscriber such as. 111 originates a call,.a line relay such as200 operates in series with his telephone set controlling the operationof other relays which causes an idle link circuit to connect to theline. As soon as the connection has been made the sleeve conductor ofthe calling line is grounded in the link circuit making theline busy toany link circuits or trunks which may select it and operatescut-offrelay 201 which releases the line relay 200; When the line isreleased at the endof the connection the removal of the ground from thesleeve conductor releases the cut-off relay and leaves the line free tobe called.

Group circuit and c-mergcncysmrt circuit.

When the relay 200 operates it causes the operation of group relayt202through a circuit from ground, front contact and left hand armature ofrelay 200, Winding of relay 202 to battery and ground Relay 202 inattracting its armatures establishes a con necti on from ground, innerright hand armature and back contact of relay 203, outer right handarmature and front contact of relay 202, conductor 20st, left handarmature and back contact ofrelay300,conductor- 301, armature and backcontact of relay 205, left hand armature and back contact of relay 206,Winding of relay 207 to battery and ground. Relay 207 becomes energizedin this circuit and then locks up in a circuit including conductor 301,the winding of relay 205; the right hand armature and front contact ofrelay 207, the

winding of relay 207 to battery and ground. Circuits are thereuponestablished for relays 2-08, and 209. The circuit for relay 208 extendsfrom grounded battery, the winding.

of relay 208, the nextto the outermost left hand armature and frontcontact of .relay 207, the front contact and inner right hand armatureor relay 202, the'back conr tact and inner right hand armature of relay203 to ground. tends from grounded battery, the Winding of relay 209,the innermost left hand armature'and'contact of relay 207, the frontcon- A circuit for relay 209 ex-- tact and right hand armature of ,relay200, t-lie:,. front contact and .left hand arn'ia-ture of relay 202, theback contact and left hand armature ,of relay 203 to ground.

Through the action ,of relays 208 and 209, the calling line is extendedto the link circuit of .Figure 3, whereupon the calling supervisoryrelay 302 is operated by the closed loop of the calling subscribersline. Relay 302 closes a circuit from ground, the Winding of relay.303the left hand armature and front contact of relay 302, right handarmature and backv contact of relay 304,

winding of relay 305 to battery and ground. Relay :305 attracts itsarmatures and places aground on conductor 306 to which relays 208 and209lock. "The ground on conductor 306 is alsoi fextended through thecontacts of relays209 and'208yto the sleeve conduc- 1elea se of relay307 a circuit is established from ground on conductor 204 through thearmature'and front, contact of relay 308, the back contact and righthand armature of relay 307, the outermost right hand armature and backcontact of-rela-y 300, the winding of relay.309, the back contact andinnernrost right ,hand armature of relay 000 to battery and ground,whereupon relay 3300 becomes energized. WVhen this ground is removed bythe subsequent release of relav 308, relay 309 remains locked up throughthe winding of relay 300 which thereupon operates. This circuit is asfollows: ground on conductor 2041-, left hand Winding of relay 300,inner left-hand armature and front contact of relay 309, Winding ofrelay 309 back contact and inner right hand armature of relay .300 tobattery and ground. As soon asrelay 300 operates the circuit is asfollows: ground on conductor 204-, the left hand Winding of relay 300,inner left hand armature and front contact of relay 309, Winding ofrelay 309, right hand winding of relay 300 to battery and grourul.

l.he'cycle of operations of relays 307 and 308 is repeated and on thenext release of relay 307, relay 309 is short-circuit and released,relay 300 being held up until relay 308 releases. This momentarily opensthe start lead30l and closes an emergency lead which advances theselection to the next link circuit. When this condition is establishedthere will be a circuit from ground on conductor 204, the left handarmature and front contact of relay 300, back contact and outer lefthand armature of relay 309, emergency lead 310, left hand ari'nature andback contact of relay 210, right hand winding of relay 206 to batteryand ground. llela becomes energized and extends condu 301 to conductor211 leading to a left hand armature of a relay 212 individual to thenext link circuit and performing the same functions as relay 206. Thuswhen a call is initiated it must be picked up by the first idle linkcircuit very quickly or the emergency circuit will operate to make eii'ective the next idle link circuit.

L mic circuit.

set of finder relays, a set of connecting relays and the apparatus forcontrolling the opera-' tions of the finder and connecting relayssupplying transmitter current and testing and ringing the called lines.

lVhen a station originates a call, the operation of a group relay suchas 202 operates a relay such as 207 through the back contact of theallotter relay such as 206. The operation of relay 207 connects therelays such as 209 to the contacts of the line relays and connects therelays such as 208 to the contacts of the group relays such as 202. Thiscauses the operation of the relay 208 corresponding to the group of tenlines in which the calling line is located and relay 209 correspondingto its position in the group. This connects, the talking circuit to thecalling supervisory relay 302 individual to the link circuit, whichoperates, operating in turn the holding relay 305. Relay 305 whenoperated closes a locking circuit for relays 208 and 209 and suppliesground for operating the cut-off relay 201 for the calling line andoperating the allotter relay 206.

Assuming that the link circuit, whose operation is being described, isany other than. the last, relay 206 looks up through its right handwinding and contact, the winding of relay 210 and the back contact ofrelay 213 of the last link circuit, this circuit being as follows:ground, armature and back contact of relay 213, front contact and righthand armature of relay 206, winding ofrelay 210, right hand winding ofrelay 206, to battery and ground. y

The operating circuit of relay 207 is opened by the operation of relay206, but relay 207 is locked up through relay 205 which operates andprevents the operation of relay 200 from operating the relaycorresponding to relay 207 of the neXt link circuit. Relay 205 which iscommon to all the links releases upon the release of relay 202 of thegroupv cuit. When the last link circuit isselected and its relay 21loperates, it locks up through its right hand Winding and contact andwinding of relay 21 i and contacts of the corresponding relays of allother link cir cuits in series. telay 213, of the last link operating,opens the locking circuit for relays corresponding to 206 and 210 in allthe other link circuits, releasing relayscorresponding to 200 of suchlink circuits as are not in actual use. The release ofrelayscorresponding to relay 210 in any other of the linkcircuitsreleases relay 213 of the last link circuit and reestabli shesthe locking circuits for the relays corresponding to 206. In case oftrouble in a link circuit which prevents relays corresponding to relay206 from. operating in the normal manner within a predetermined time,the actionof the emergency start circuit grounds the emergency startlead 310 which operates relay 200 through its right hand windingand atthe same time opens the regular start lead 301 and releases relays 207and 205. As soon s the action of the ei'i'iergency circuit removes theground from the emergency start lead relay 210 operates and relay 2120fthe next link is operated.

When the holding relay 305 operates it closes the operating circuit forrelay 3l2.

Relay 312, however, does not operate since it is short-circuited by acontact of the supervisory relay 202. When the subscriber operatesl'iisdial, relay 302 releases in responseto each interruption of the linecircuit by the dial springs, permitting relay 312 to operate. Theoperating circuit for relay 312 is then as follows: grounded battery,resistance 314i, winding of relay 312,

back contact and inner right hand armature of relay 313, conductor 306,trout contact and right hand armatureof relay 305 to ground. Relay 312,in operating, operates magnet 315 which steps the direction switch 1ahead. Magnet 315 controls an extra armature which closes a contact tooperate magnet 316. The armature of magnet 315 which controls itscontacts is slow in releasing, so

thatit does not fall back on a'momentary release of relay 312, althoughthe other armature follows the impulses received from relay 312 andsteps the switch. ahead. Magnet 316, when it operates, permits theholding pawl of the switch to engage with its ratchet so that the switchdoes not release so long as nn'ignet 316 is energized. When the dialcomes "to rest relay 302 remains operated and relay 312 is released longenough to permit both armatures of magnet 315 to release. Magnet 316 isslow to release so that it remains operated momentarily after therelease of relay 315, grounding the group brush 317 and operating theconnecting relay associated with the group of ten lines in which thecalled line is located We will asleading to relay 215.- In this mannerrelay 215 will become operated. The original operating circuit of relayis opened on the release of nmgnet- 316 but relay 215 remains operatedin series with relay 319 which itself becomes energized. This circuit isas follows: ground on conductor 306, winding of relay 319, conductor320, right hand armature and front contact of relay 215, winding ofrelay 215 to battery and ground. The release of magnet 316 removes thepawl from engagement with its ratchet and permits the direction switchto return to normal.

l lelays and 312 and magnets and 316 function in the same mannerresponsive to the second operation of the dial but as relay 319 is nowoperated. magnet 316 in operating, energizes relay 321 in a circuitextending from ground, right hand armature and front contact of magnet310, innermost right hand armature and front con-- (act of relay 319,winding of relay 321 to battery and ground. When magnet 310 releasesafter the dial comes to rest the units brush is grounded, operating theunits relay corresponding to the position of the called line in itsgroup. In accordance with our assumption this unit series of impulsesconsists of a single interruption of the calling line circuit and brush322 comes to rest on its first contact and grounds conductor 323operating thereby units relay 216.

Assuming the called line. 191 to be bus-1; and the cut-off relay 2-47 tobe operated by ground on the sleeve 2&8 of the called line. then uponthe operation of relays 215 and 216 a circuit will be established fromground on the sleeve 2418 of the called line through the correspondingcontacts of relays 215 and 210 to the sleeve conductor 32a of the linkcircuit through the left hand armature and front contactof relay 321,the normal contacts of the inner left hand armature of relay 313, thewinding of relay 313 to battery and ground. Relay 313 operates and locksup to ground on conductor 306 in turn locking up relay 321 in a circuitfrom battery, winding of relay 321, front contact and armatureof relay321, front contact and innermost right hand armature of relay 313 toground on conductor 306. Relay 313 also opens the circuit ofrelay 312 toprevent the direction switch from responding to any further movement ofthe dial and connects busy tone through the condenser 326 to the callingsubscriber. The path of the busy tone is as follows: from conductor 327,leading from a sourceof busy tone through the front contact andoutermost left hand arm ature of relay 313, conductor 323, back con--tact and outermost right hand armature of relay 325, condenser 326,right hand winding of relay 329 to battery, whence by 111- ductance inthe windings of relay 329 busy magnet- 330 to battery and ground. Magnet1 330 attracts its armature and automatically interrupts its circuit.This causes a rapid automatic vibration of the armature of magnet 330which so effects the potential'on conductor 32'? that a tone is set upthereon.

Assuming the called line to be idle, relay 313 does not operate becausebattery connected to its winding is opposed by battery connectedtothewinding of cut-on relay 247. Upon the release of magnet 310, relay321 becomes deenergized. This connects the slee 'e 324- through a backcontact of relay to a winding of supervisory relay 329 which becomesoperated and causes the operation of relay 313. A circuit for theenergization of relay 329 is as follows: from grounded battery, thewinding of cut-ofli' relay 24:7, sleeve conductor 2 18, through thecorresponding contacts of relays 215 and 216, conductor 324, left handarmature and back contact of relay 321, normal contact of the innermostright hand armature of relay 325, left hand winding. of relay 329 toground. Relay 329 inattracting its armature extends the ground onconductor 300 through its contact and armature to the normal contacts ofthe innermostleft hand armature of relay 313, the winding of relay 313to battery and, ground. Relay 313 becomes energized and locks up in thecircuit previously traced.

Since relay 321 is deenergized at this time a circuit will beestablished for relay 325, said circuit extending from grounded battery,

winding of relay 325, back contact and right.

hand. armature of relay 321, front contact and innermost right handarmature of relay 313 to ground on conductor 306. Relay 325 transfersthe sleeve conductor 3 1 from the left hand winding of relay 329 to aground connection on conductor 306. Relay 325 also connects the tip andring of the called line to the armatures of ringing relay 331.

Interrupted ringing current is now supplied to the called line from thesource of such ringing current shown in the right ture of relay 331,front contact and innermost left hand armature ofrelay 325 throughcontacts of relays 216 and 215 over the loop of the called substation191, back through the contacts of relays'215 and216,

the outermost left hand armature and front:

vof the receiver at the called substation.

Thereupon relay attracts its armatures and locks itself in a circuitincluding its right hand winding, its front contact and innermost righthand armature to ground on conductor 306. Through itsleft hand armaturesit extends the called line to con trol of the called supervisory relay329. Talking current is supplied to the called line through the windingsof relay 329, and to the calling line through the windings of relay 302.The connection is now in a stable condition and conversation may now becarried on. l

At the end of the conversation the re lease of the apparatus is effectedby the calling station replacing its receiver and causing thedeenergization of relay 302. Relay 302 iii-retracting its armaturesreleases its control over the holding relay 305 and when after aninterval this relay becomes released, all of the relays under itscontrol return to normal and the connection is restored.

In case the trunk code is dialed, relay 304 becomes operated in place ofone of the relays corresponding to relay 215 and relay 304 looks up in acircuit including battery, its winding, its front contact and innermostleft hand armature and the front contact holding relay 305 togroundJ Thetrunk relay 304 opens the operating circuit of the holding relay 305 andconnects ground froin the front contact of relay 302 to a relay in thefirst idle trunk circuit. circuit extends from ground, winding of relay303, left hand'armature and front contact of relay 302, right handarmature and front contact of relay 304, conductor 334, innermost lefthand armature and back contact of relay 400, winding of relay to batteryand ground and in parallel therewith through the back contact andoutermost right hand armature of relay 400 to the winding of holdingrelay 401 to batterv and ground.

Upon the operation of relay 304, a circuit is established for theoperation of relav 335 asfollows: ground, fourth arina-V t tre of theset of left hand armatures of relay 208 individual to line 111,outermost left hand armature and front contact of relay 209, conductor217, outermost left and left hand armature of the This hand armature andfront contact of relay 304, left hand winding of relay 335', backcontact and armature of relay 336to b'attcry and ground. Relay becomesenergized and extends the ground on conductor 217 through. its outermostleft hand armature, conductor 337, outermost right hand armature andfront contact of relay 208, conductor 218, armature 101 of relay 100 andfront contact co-operating with said armature, winding of relay 102 tobattery and ground causing the energization of said relay 102. Acircuitis also established-from ground on conductor 217 through the innermostleft hand armature and front con tact of relay 335, conductor 338,outermost right hand armature and front contact of relay 209, conductor219, innermost left hand armature and front contact of relay 100,winding of relay 103 to battery and ground causing the energization ofsaid rela v 103. Relay 335 also completes'a circuit from ground onconductor 311, right hand armature and front contact of relay 335, righthand winding of relay 335, Wind ing of relay 336 to battery and ground;whereby relay 336 is energized to open the original energizingcircuit ofrelay Relay 335 is individual to the link circuit but relay 336 iscommon to all link circuits so that when relay 336 operates it preventsthe operation of any other relay corresponding to relay 335 until theone here shown becomes deenergized. it

The operation of relays 102 and 103 extends the calling line to thetrunk shown in Figure 4. Relay 102 is then looked up in a circuit fromground, the right hand armature and front contact of relay 401, contacts402 of key 403, back contact and outermost right hand armature of relay404, conductor 405, front contact and armature of relay 102, winding ofrelay-102 to battery and ground. Relay 103 isalso locked up in a circuitincluding ground, right hand armature and front contact of relay 401,contacts 402 of key 403, conductor 406, front contact and armature ofrelay 103, winding of relay 103 to battery and ground. Ground was alsoextended from conductor 406, 'through the right hand armature and frontcontact of relay 100, conductor 104, right hand winding of relay 407 tobattery and ground. Relay 407 locks up through its front contact andinnermost right hand'armature to ground on conductor 406. p r

Relay 401 also places ground on conductor 408 for a purpose which willappear hereafter. The busy lam 409 is illuminatedin response to theenergization of relay 401.

Relay 400 is short-eircuited through its own back contacts and by theground on'conduc-' tor334'and will not become energized until relay 302releases, It will be remembered 428 in operating opens the circuit ofrelay 413- i As soon as the call has been amnvorcd by an operator, relay-32 operatesin a circuit including grouinl, the tip conductor of thetrunk at the central office, contacts 423 of lie 424, contacts 434 ofkey 430, right and left hand windings of relay 432 in. series, contactsof l-zey 424. ring conductor of the trunk at the central oi'lico togrounded battery. Relay 432 in operatingcauses the operation of relay436. The rela? 4336 con i'iects relay 437 in a circuit which may betraced from grounded battery, Windingof relay 437, contacts 433 of lrcy430, front contact and outermost left hand armature of relay 423, lefthand rinature and front contact of relay 436 to ground. Relay 43".- inoperating extends the calling line to the central oiiice. Relay 420 iscut off and dermergized but relay 401 is held operated by the outermostleft hand arn'iature and front contact ofrelay 437,. whereupon relay 439operates in series with the calling line and in turn causes theoperation of relay 440. Relay 440 opens the circuit of relay 432 andplaces a non-inductive shunt 441 across the Winding of the supervisoryrelay 439. Relay 436 is maintained operated by relay 439. The connectionis now in a stable condition and the subscriber may converse with theoperator at the central ofi'ice.

lVhen the subscriber hangs up, relays 439 and 440 release permittingrelay 432 to operate which prevents the release of relay 436. The highresistance of relay 432 releases the supervisory relay at the centraloffice. As soon as the disconnection. takes place at the central office,relay 432 releases,

releasing relay 436. This releases relay 437' which in turn releasesrelay 401 and then in turn releases the reinainii'ig operated relays ofthe circuit. i

If the operator should disconnect before the subscriber hangs up, relays439 and 440 release, but relay 432 does not operate and relay 436releases. This releases relay 43? and permits relay 420 to operate. Thisholds up relay 401 and grounds the tip side of the line operating theline relay again at the central office and relighting' the line lamp.When the operator restores the connection;

relays 432, 420 releases.

436, and 4.37 operate and relay Incoming calls.

Then an operator plugs into a trunk Wl'tli a cord circuit, relay 432operates, operating ates and locks up, lighting the line lamp 442.

innermost left hand armature of relay 422,

normal contacts of the innermost left hand armature-of relay 444,conductor 445, right hand armature and front contact of relay. 436 toground. Rela-y 433 looks up in a circuit including battery and ground,its left hand Winding, its left hand armature and front contact toground over the circuit just traced. The attendant subscriber at station490 answers by means of the listening key 446, operating thereby relay422 whichrelea'sos relay 433 and extinguishes v line lamp 442. Thecircuit for relay 422 may be traced from grounded battery, winding ofrelay 422, contacts 447 of key 446 to; ground. Guard lamp 448 lights asit is in multiple with the Winding of relay 422. Ree

lay 439 operates, operating relay 440 Which bridges the non-inductiveshunt 441 across the Winding of relay 439. Retardation coil 449 Wasbridged across the line in series with the low resistance Winding ofrelay 432'by the operation of relay 422 and a short-circuit isremovedfrom its middle high resistance Winding by the operation of relay 440.Relay 432 may release but relay 436 is held operatedby contacts of relay439.

To extend the'call to a station, the attendant subscriber operates thestation key which comprises the left hand contacts of key 430. Thisopens the circuit of relay 428 and operates relay 105. The circuit forrclay=105 may be traced from grounded bat tery, winding of relay 105,conductor 106, normal contacts of the inner right hand armature of relay416, contacts 450 of key 430, contacts 451 ofkey 446 to ground. Relay105 connects the trunk to thecommon selecting apparatus and operatesrelay 404 in a circuit including grounded battery, Winding of relay 404,conductor 452 innermost right hand armature and front contact of a relay105' to ground. Relay 404 When operating transfers the attendantsuhscribers' telephoneset to the other, side of the contacts of relay43'? thereby operating relay 420. Relays 439 and. 440 release, but relay422 remains operated. The release of relay 440' short-circuits the highresistance Winding of the retardation coil 449 andrelay 432 operates andprevents the release of relay 436. Relay 401 operates and. closes anoperating circuit for relay 107 which however is short-circuited at thistime so that it does not operate. The circuit for causing this may betraced from the top side of relay 107 through contacts 108 of relay 105,conductor 109 front contact and innermost right hand armature of relay422, right hand armature and front contact of relay 420 to ground andfrom the lower terminal of relay 107 to contacts 112 of relay 105,conductor 408, to ground on the left hand armature of relay 401.

The attendant subscriber now operates her dial to select the desirednumber and relay 420 releases at each interruption of the circuit by thedial springs, permitting relay 107'to operate. llelay 107 in operating,op crates stepping magnet 113 of the switch which steps the wiper ahead.carries an extra armature which controls a contact which. operatesmagnet 114. Magnet 114 in operating allows the holding pawl of theswitch to engage with its ratchet and closes a circut through itsinnermost right hand armature and front contact and the back contact ofrelay 115 to group brush 116. The armature of'ina-gnet 113 whichoperates the contacts is sluggish so that it does not release when relay107 is momentarily re leased in response to the dial impulses althoughthe other armature follows the impulses received from relay 107 andadvances the switch to the operating position. When the dial comes torest, relay 107, is released long enough to permit both arlnatures ofmagnet 1 13'to release. Magnet 114 is sluggish so that it remainsoperated momentarily so that the group brush 116 is grounded, operatingthe connecting relay associated with the group often lines containingthe called line. i

Wewill assume that a call is being set up to the subscriber at station110; therefore the set of impulses for moving the group brush 116consists of a single interruption of the attendant subscribers linecircuit and group brush 116 comes to rest on its first contact.

Uponthe release of magnet 113, conductor.

117 is grounded, causing the operation of relay 102. The circuit for theenergization of relay 102 may be traced from ground, the armature andback contact of magnet 113,

the innermost right hand armature and front contact of magnet 114, theleft hand armature and back contact of relay 115 group brush 116,conductor 117, contacts 118 of relay 105, winding of relay 102 tobattery and ground. Relay 102 looks up toground on conductor 405, whichground is supplied from the left hand armature and front contact ofrelay 401, conductor .408, contacts 112 of relay 105, winding of relay115, contacts 119 of relay 105, to conductor 405. Relay 115 is operatedin this circuit. In a short interval magnet 114 retracts its armaturesMagnet 113' and permits the switch to return to normal. Relays 420, 107and magnets 113 and 114 function in the same i'uanucr in response to thesecond operation of the dial but as the relay 115 is now operated theoperation of magnet 11 i. operates relay 410 in a circuit includinggrounded battery relay 410, condin-tor outeru'iost right hand armatureand front contact of relay 105 front contact and outermost right handarmature of magnet 114, front contact and right hand armature of relay115 to ground. When magnet 113 releases it grounds the units brush 120,operating the units relay corresponding to the position in its group ofthe called line.

In accordance with our assumption, this last series of impulses consistsof ten interruptions of the attendant subscribers line. This causes theunits brush 120 to come to rest on its tenth contact and groundconductor 121 whereupon relay 122 is operated. The circuit for theoperation ofrelay 122 may be traced as follows: grounded battery, relay122, contacts 123 of relay 105, conductor 121, units brush 120, frontcontact and left hand. armature of relay 115, front contact and innerright hand armature of magnet 114,

back contact of magnet 113 to ground. Re-' 122, sleeve conductor 413,left hand armature and front contact ofrelay 410, normal contacts of theinner left hand armature of relay 416. contacts 417 of key 403. windingof relay 416 to battery and ground.

If the line is busy the sleeve is grounded so that relay 416 operatesand locks up, in turn locking up relay 410. The operation of relay 416also releases relay 105. leaving relay 107 directly under control of thestation key comprising the left hand contacts of key 430. The release ofrelay 105 opens the holding circuit for relay 102, but the groundconnection for locking up relay 102 is now furnished by the operation ofrelay 416.

In case the line is not busy, relay 416 does not operate and relay 410releases upon the releaseof magnet 114 connecting the sleeve through theresistance 411 and relay 412 to ground. Relay 412 operates in serieswith the cut-off relay of the line and locks up through relay 416 whichopcrates, cutting off and releasing relay 105. As relay 410 is nownormal and relay 412 is operated, the operation of relay'416 operatesrelay 414 which cuts the sleeve of plied to the called line through the;back contact and left hand winding of relay 407. Direct current issupplied to the line through the winding of relay 407 during the silentintervals and is superimposed on the alternating current during theringing intervals. The operating circuitof the ringing interrupter-s isclosed bythe operation of relay 400. I i

The attendant may now restore her keys. Relay 407 does not operate onthe current which passes through the subscribers bell but as soon as thesubscriber answers he closes a path through his telephone set for directcurrent which operates relay 407. Relay 407 locks up through its righthand winding and connects the subscriber through to relay 420 and opensthe operating cirunit of the ringing interrupters. Relay 420 operates,operating relay 401 and as, the station key has been restored to normal,relay 428 also operates. As relay 436 is operated, this causes theoperation of relay 437 cutting the line through to the cen tral otliceand operating relays 439 and 440. As relay 422 is operated,'theoperation of relay 440 causes the operation of relay 444, the circuitfor which may be traced from grounded battery, left hand winding of relay 444, outer left hand armature and front contact of relay 422, outerright hand armature and front contact of relay 428, front contact andinner left hand armature of relay 440 to ground. Relay 444 locks up toground on conductor 406 and places the locking circuit of relay 422under the control of relay 440 and also operates relay 455 under thecontrol of relay 440 which eirtinguishes the guard lamp 448. Theoperation of relay 440 also bridges the noniuductive shunt 441 acrossthe winding of the supervisory relay 439 and removes the short-circuitfrom the high resistance winding of the retardation coil 449. The connection is now in a stable condition and conversation may proceed.

When the subscriber hangs up relays 439 and 440 release releasing 1nturn relays and 455. Relay 432 operates preventing the release of relay436. fThe bridge through the retardation coil has removed from the lineby the release of relays 422 and 455 and the high resistance of relay432 permits the release of the supervisory relay at the central office.When the disconnection takes place at. the central oflicei relay 432releases, releasing relay 436. This releases relay 437 and relay 401which turn release all other operated relays and restores the circuittonormal.

The subscriber may recall the attendant by depressing the switch hoolrmomentarily or operating his dial, thus releasing relay 440 momentarily,which releases relay 422. As relay 444re1na1ns operated line lamp.

442 is lighted but relay 455 remains operated preventing the guard lamp443 from lighting. Relay 455 isslow in releasing so as toprevent'disturbance oi" the apparatus at the central oflice by amomentary interruption of the circuit through the subscribers telephone.The attendant subscriber answers by operating her listening key 440which bridges her telephone set across the line and causes relay'422 tooperate and lock up. In case she has occasion to trans fer the call toanother line sheoperates a release key 403 which releases'relays 423,444, 416, 412, 414, 407, 102 and 122. Relay 455 is released by therelease of relay 444 a and guard lamp 448 lights. The attendant -may nowoperate her station keycomprising the right hand contacts of key 430 andselect another station in the manner already described. y

In case the line whichthe attendantselects is busy she may, if theimportance of the incoming call appears to justify it, break in upon theconversation by operating key 419. This releases relay 410 and cuts 03'the busy tone and operates the contacts of relays 414 and 407 so thatthe attendants telephoneset is connected to the called liner iTherelease of key 419 does not operate relay 410 again so'thatthe sleeve ofthe line 412. Relay 412, however, does not operate When the called linebecomes free, the reis connected through resistance 411 and relay fmoval of the ground from itssleeve permits relay 412 to operateand lockup through relay 416 and operate relay 414. The line .is now connectedthrough to relay1407jso' that the subscribers bell rings and the remainder ofthe operation. is the same as it the line had not been busy.In case the attendant does not wish to wait for the line to become idle,she may operate the release key 403. after releasing key 419 and thenselect another line.

In case the attendant subscriber receives an incomingfcall which isnotextended to a station she may give the disconnectsignal to thecentral ofiice by] restoring her listening key andoperating thedisconnect key 424. This releases relay 422 opening the bridge throughthe retardation coil The disconnect key 424 may be used as aflashinglrey for signaling the operator by operatingit when thelistening key is operated. This opens the line to the central officereleasing the supervisory relay there-- tag at'but relay 439; remains.operated in serieswith the telephone set and resistances 456. and 457,preventingtherelease ofrelay 436.

OaZZs originated by attendant subscriber.

The attendant subscriber may originate a call to the centralofliceoperating the listening key. This groundsthe tip of the;

trunk through aback contact ofrelay 436 and a back contact. of relay 404operating the line relay at the central office. same time thedepressionof the listening key 446 operates relay 422 which groundsthe,sleeve of the ltrunk lighting the busyla np 409 and operatingwrelay 400.Vtlhen the operator at. the. central oflice answers relay.

439 operates, operating in turnrelays440.

and 436.

After, the. attendant has originated a. call to the centralofiice, shemayextend it to any stationjustas: if itwere aninconiing call.

The attendant may; call any station. over a trunk by operating. the.station key and.

the listening. key and selecting; the. station in the samemannerasdescribed for-the incommg call. The operation of relay 404 cuts,off the. calling in groundrso'that the linerelay at thecentraloffice isnot operated. The. callmay be -extended to the central office byrestoring the station key and leaving the listening key operated untilthe-central office has. answered.

In case of a failure in thebatterysupply. within this system theattendant may call the central oiiice by operating. the. central oflicekey comprising" the right hand-cone tacts of key 430, the listening key446. and the. emergency key 45,8. The central ofiice key in additiontocutt-ing off the bridges across the circuit, places. a noninductiVeshunt across the winding ofrelay 439. Under this condition relay-459operates as soon as the operator atthe centralofiicean swers, andvremoves, the callin gein ground from the line.

Ring mgcircuit;

Whenever any link circuit or trunk circuit is 1n. the ring ng conditionrelay 340 is operated. Th s'closes a. circult for operating relay 341which operates. and-locks up and operates relay 34 2, Relay 342 opens:

" the operating circuitofrelay 341 and locks up andshort-cirouitsandreleases relay. 341.

Relay 341 in, releasing opens the operating;

circuit of relay. 342 and' short-circuits andreleases it. The releaseofrelay 342allows:

relay 341 to operate again and this .cyc leof. operations continues. aslong as. relay 340 remainsoperated. Ground isconnected first to oneandthen to the other of the-primary. Windingsof the ringing transformer-343by, the contacts of relay 342 so that-ani alter.- nating current isinduced in the secondary At the Winding ofthe transformer 343 as-longas,

the common point of the primaries is connected to. battery through thefront contact of relay 344 and the back contact ofrelay 345. Relay 340also closes an operating circuit for relay 346. which operates andlockstup and operates. inturn relay 347.

Relay 347 inoperating opens the operating circuit of relay 346 andshort-circuits and releases it.. Relay 346 in releasing releases relay34 7, thispermits relay 34.6 to operate again and the cycle ofoperations is repeated as long asrelay 340 remains operated. Assoont asrelay 340 operates, it operates relay 344 through the back contactsofrelays 347 and 34'5connecting battery to the pri mary. windings of theringing transformer 343;- WhenQrelay 347 operates relay 344-is.

locked up through the righthandwinding ofrelay 345 Relay 345 operatesremoving the. shortcircuit from itsleft hand winding andcuts oti batteryfrom the ringing transformer 343. When relay 347- releases it short=circuits. and releases relay 344 but relay 3451'remains locked up throughitsle ft Tone circa-it.

VVheneVer relay 302 of a link circuit or relay 420 of atrunkcircuitisoperated relay 303 operatesand closes a circuit throughthe back contact and winding of. relay 330. Relay v330 operates. as. abuzzer and supplies busy tone and dial tonev through the link andtrunkcircuits.

Buzzer circuit.

Battery is supplied to the line lamps ofthe tr-unks:"through the relay339 which'operateswhenever a line-lamp is lighted and sounds the buzzer.The key-348 B furnished by means. of which the buzzer may be silenced;even. though the line lamp is burning.. VZhen the relay, 339 is operatedand key. 338-isenormal" a circuit is established 3 from: ground, the.armature and. front con-- tact of relay-33 9,, the left hand. Windingofrelay 349; the back contact anctarmaturc of relay- 350," the right handwinding of relay 349 togrounded battery. Relay 350 actsas a buzzerand?createsan:audible tone. to attract the attentionofl the attendantsubscriber; T

What is claimed is:

said lines, a plurality of saidrelays being employed in establishinga-connection, direc- "tively operable means for energizing a pluralityof said relays-normally eifective to energize one of-said' relays, andmeans responsive to the energization of said one of said relays forcontrolling said energizing means. i

2. In a telphone system, telephone lines,

groups of relays for establishing connections to said lines, a relay ofeach groupbeing employed in establishing a connection, directivelyoperable means for selectively energizing said relays, a relayassociated with said means, means responsive to the selectiveenergization of a connecting relay of one group for energizing said lastrelay, and means controlled by said last relay for changing the controlof said energizing means from one group of said connecting relays toanother group of said connecting relays.

3. Ina telephone system, telephone lines, groups of relays forestablishing connections to said lines, a direction switch forpilotingsaid connections, and a relay associated with said direction switchresponsive to the energization of a connecting relay in one of saidgroups for controlling said direction switch to cause energization of'aconnecting relay in another of said groups.

at. In a telephone system, telephone lines, switching devices havingpermanently paired'primary and secondary contacts for establishingconnections to said lines, means for operating said devices to establishconnections to busy lines, and means responsive to the removal of thebusy condition to automatically render such connections effective.

5. Ina telephone system, a plurality of telephone lines, an operatorstrunk, a central oliice trunk, switching devices having permanentlypaired primary and secondary contacts for interconnecting said lines andtrunks, means for operating said devices to establish connections tobusy lines, and means responsive to the removal of the busy condition toautomatically render such connections efl ective.

6. In a telephone system, telephone lines, an operators trunk, switchingdevices having permanently paired primary and secondary contacts forinterconnecting said lines and said trunk, means under control of saidoperators trunk for establishing a connection to a busy line, and meansrespona sive to the removal of the busy condition to automaticallyrender such connection efiect-ive. i

7. Ina telephone system, telephone lines, an operators trunk, switchingdevices having permanently paired primary and secondary contacts forinterconnecting said lines and said trunk, n cans under control of saidoperators trunk for controlling said devices for establishing aconnection to a busy line, and means responsive to the removal of thebusy condition to automatically render such connection effective. 7

8.In a telephone system, telephone lines, an operators trunk, switchingdevices having pern'ianently paired primary and secondary contacts forinterconnecting said lines and said trunk, a direction switch forcontrolling said devices, means for operating said direction switch tocause one of said devices to establish a connection to a busy line, andmeans responsive to the removal of the busy condition for rendering saidconnection effective.

9. In a telephone system, telephone lines, an operators trunk, a sendingdial associated with each of said lines and with said trunk, switchingdevices having permanently paired primary andsecondary contacts forestablishing interconnections between said lines and said trunk, adirection switch separate from said interconnections for controllingsaid devices, said direction switch being responsive to the manipulationof said dials, and means responsive to one operation of a said switchingdevice for controlling sain direction switch.

10. in a telephone system, telephone lines, an operators trunk, asending dial individally associated, with each of said lines and withsaid trunk, groups of switching devices having permanently pairedprimary and secondary contacts for establishing interconni-ictionsbetween said lines and said trunk, a switching deviceo't each groupbeing required to complete a connection, a direc ion switch separatefrom said interconnections ior controlling said devices, said directionswitch being responsive to the manipulation of said dials, and meansindividual to said direction switch responsive to the actuation of aswitching device of one of said groups under the control of said Idirection switch for transferring the control off said direction switchto another otsaid groups of switching devices.

11. In a telephone system, telephone lines, relays for establishingconnections between said lines, a plurality of said relays beingemployed in establishing a connection, direction switch separate fromsaid established connection for controlling the operation of saidrelays, said direction switch being normally effective to cause theenergization of one of said relays, and a relay associated with saiddirection switch responsive to the energization of said one of saidrelays for transferring the control of said switch to another of saidrelays.

12. Ina telephone system, telephone lines, relays for establishingconnections between said lines,.said relays being, divided into groupsand a relay of each group being employed in establishing a connection, adirection switch separate from said established connection forcontrolling the operation of said relays, said direction switch beingnormally effective to cause the energization of the relays of one ofsaid groups,

and a relay associated with said direction switch responsive to theenergization of one of said relays of said one of said groups fortransferring the control of said switch to another of said groups.

13. In a telephone system, a telephone line, a central 'oflice trunk, arelay under control of said line for placing a calling condition'on saidtrunk, a source of current for energizing said relay, other means undercontrol of said line for placing a calling condition on said trunk uponfailure of said source of current, and a normally inoperative relaycontrolled in part by said means, said last relay being responsive tothe extension of saidrcentral otlice trunk to remove said callingcondition.

14. In a telephone system, a telephone line, aoentral oitice trunk,means at one end of said trunk for connecting said line'thereto, meansat the other end of said trunk for indicating av calling conditionthereon and for extending said trunk, means associated with said linefor placing a calling condition on said trunk, a relay for removing saidcalling condition responsive to the extension of said trunk, a souree ofcurrent for energizing said relay, a normally inoperative relayindependent of said source of current for removing said callingcondition, and meansior-rendering said last relay operative upon failureof said source 0t 1 current.

15. In a telephonesystem, telephone lines, link circuits, switchingdevices having, permanently paired primary and secondary contacts forconnecting said lines to said links, a mechanism normally eiiect-ive toren der said links selectable in the order of their sequence, a startingcircuit for governingthe control of said switching devices, saidstarting circuit including a relay arrangement common to said linkcircuits arranged to measure time. against the operation of saidswitching devices to chai'ige the order of selectabil-ity of said linksand to transfer said starting circuit to another switchingdevice-upon:the -failure of one of said devices't'o connect a line towalinkwithin a predetermined time 16. In: a t'elephonesystem, telephonelines, link circuits, switching devices having permanently paired?primary and" secondary contacts fonconnectingisaid lines to said links,a mechanism normally eflective to render said links selectable in theorder of their sequence; a. starting circuit for controlling saidswitching devices, said starting circuit including a relay arrangementcomprising a plurality: of slow relays common to-said link, circuits"arranged to measure time against the-operation of said switching devicesto change the order of selectability of said' links:and to transfer saidstarting circuit to another switching device upon the failure of one ofsaid devices to connect aline to alink within predetermned time; i r

17. 111 a telephone system, telephonelines, lllllLCll'CLlltS, switchingdevices having permanently paired primary and secondary contacts forconnectingsaidlinesto said links, a starting circuit arranged tonormally cause the operation of afirst-in-order switching device, saidstarting circuit having associated with. it. a relay arrangement formeasuringtime,v said relay arrangement being arranged to transfersaid'starting circuit to a second-in-order switching device upon the failureof said first-in-order switching device; to operate Within a"predeterminedtime, to thereafter transfer said starting circuit to: athird in-order switching device upon the failure of said second in-orderswitching device to operate within a predeterminedtime, and to"thereafter transfer said starting circuit in the. manner aforesaid anydesired number of times.

In witness where-0L1 hereunto subscribe my name this 8th. day of JanuaryA. 1);,

EDlVAB-D E. HINRIGHSEN;

